Comparison of the localized power loss and flux distribution in the butt and lap and mitred overlap corner configurations

The most common type of joint in large single-phase transformer cores is the 45° mitred overlap, but also important in smaller cores is the simpler butt and lap joint. The localized power loss and flux distribution has been measured in these two types of joint built from the same size and type of gain-oriented silicon-iron laminations. In both joints, the localized loss rose to double the nominal limb loss in some areas due to the presence of normal flux or rotational flux. The rotational flux occuring mainly in the butt and lap joint caused it to be the less efficient joint. The butt and lap joint was 18% less efficient than the mitred overlap joint at 1.5 T (50 Hz) built in the cores with 15-cm wide laminations.